1. Field of the Invention
The present invention relates to a transmission rate control method for controlling a transmission rate of uplink user data at a mobile station based on a received relative transmission rate of the uplink user data which is transmitted from a radio base station via a relative transmission rate control channel, and a mobile station used in the transmission rate control method.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
In the mobile communication system to which the “Enhanced Uplink” is applied, the mobile station UE is configured to increase the transmission rate of the uplink user data (to be exact, a transmission power ratio of an “Enhanced Dedicated Physical Data Channel (E-DPDCH)” to a “Dedicated Physical Control Channel (DPCCH)”, or an E-DPDCH transmission power offset), when the mobile station UE receives “Up command (+1)” which is transmitted from the radio base station Node B via an “Enhanced Relative Grant Channel (E-RGCH)”.
On the other hand, when the uplink user data to be transmitted become empty in the transmission buffer of the mobile station UE, the radio base station Node B is configure to transmit “DTX” via the E-RGCH (that is, the radio base station Node B transmits nothing). Thus, the transmission rate of the uplink user data of the mobile station UE can be maintained.
However, in the above case, the mobile station UE may determine that “Down command (−1)” is received at the mobile station UE, even when the radio base station Node B transmits “DTX”.
When the mobile station UE determines that “Down command (−1)”, is received, the mobile station UE is configured to decrease the previously used transmission rate of the uplink user data by a certain value.
In other words, in the above case, the transmission rate of the uplink user data is decreased by a predetermined value even though the mobile station UE transmits nothing in the previous TTI (Transmission Time Interval). Accordingly, there has been a problem that the transmission rate of the uplink user data cannot be maintained.
As a result, in the above case, the radio base station Node B is required to perform the processing, such as notifying an absolute transmission rate of the uplink user data via an “Enhanced Absolute Grant Channel (E-AGCH)”, which causes the transmission delay.